This work is aimed at studying the aggregate state effect on the decomposition temperature of the copper formate (FC)−dimethyl sulfoxide (DMSO) complex during the transition from a solid state to a solution in DMSO. Methods of quantum chemical (QC) calculation were used along with experimental diagnostics, including differential scanning calorimetry (DSC), spectrophotometry, X-ray diffraction analysis (XRD), and thermogravimetric analysis (TGA). Based on the results of the study, the mechanism of decrease in the reduction temperature during the transition of the DMSO complex from a solid state to a solution was established and described. The inhibitory role of water in the mechanism of decomposition of the dissolved FC complex was revealed and described. The results of the study are in good agreement with the literature data, and they allow revealing key aspects that open up ways to create high-quality copper structures formed by inkjet printing.